The long term goal of this proposal is to help clarify the effects of damage to the thalamus and cortex on somatic sensation by identifying the specific thalamo-cortical structures responsible for the use of temperature cures on object recognition. The immediate aim is to use the ablation technique to elucidate the role(s) of the SI and SII cortex and the ventrobasal nuclei in the thermal discriminability of the rat. Previous ablation studies on rats have yielded negative results; but these studies have been criticized for using thermal differences too large to detect underlying deficits, and for failing to systematically study the rat's ability to use its most sensitive somatic areas (face or tongue) to perform the tasks. Although most electrophysiological studies reporting the presence of thermosensitive units in the thalamus or cortex have stimulated the face or tongue, no study has investigated the effects of the ablations on the ability of these body parts to make thermal discriminations. The proposed research is designed to avoid these criticisms by requiring the rat to use its tongue to make relatively fine temperature discriminations. The design is adapted from previous studies by the principal investigator in which similar ablations in monkeys produced positive results. Food-deprived rats will be trained to select the maze-arm adjacent to the cooler of two choice-point stimuli in order to obtain food reward. Large initial differences between stimuli will be gradually reduced by a modified method of limits until a 1 degree C difference is successfully discriminated. The rats will then be subjected to one of the following bilateral lesions and then tested postop: (1) SI, (2) SII, (3) SI and SII, (4) nucleus ventralis posteromedialis (VPM), (5) nucleus parafascicularis (Pf), (6) VPM and Pf, r (7) sham. Since so few ablation studies have been concerned with thermal sensibility, this proposal, if funded, should enhance our understanding of the thalamo-cortical substrate of the temperature sense.